Production of abietic alcohol



Patented Apr. 5, 1938 UNITED STATES PATENT OFFICE PRODUCTION OF ABIETIC ALCOHOL No Drawing. Application September 25, 1935, Serial No. 42,107

2 Claims.

This invention relates to the production of high molecular weight alcohols and more particularly to the reduction of esters of high molecular weight acids by reaction with alkali metal and a hydrolytic alcohol.

This application is a continuation in part of our copending application Serial No. 729,900 now United States Patent 2,019,022 dated October 29, 1935.

The reduction of esters of high molecular weight acids to form high molecular weight alcohols by reacting the esters with alkali metal and a lower aliphatic alcohol in a solution of the lower alcohol has long been known. The method originally proposed (United States Patent 868,252) consisted in placing pieces of alkali metal in a closed container and slowly adding thereto an ethyl alcohol solution of the ester to be reduced. A large excess of the solvent alcohol and the alkali metal were used. After the reaction was completed excess alkali metal and the alkali metal compounds were decomposed by treating with alcohol and water and the higher alcohol formed was recovered by distillation. The reactions involved may be represented as follows:

This method has not been adapted for economical commercial practice because of low yield of product and poor reduction efiiciency; that is, a considerable portion of the alkali metal used is consumed with the evolution of hydrogen from the solvent alcohol rather than being used to reduce the ester. Another disadvantage of the process as originall roposed is that generally as the reaction proceeds the viscosity of the reaction mixture progressively increases until a highly viscous gel-like mass is produced and the surface of the alkali metal becomes coated over and is rendered unreactive.

In order to overcome the above disadvantages,

various improvements have been proposed from time to time. One such improvement consists in the use of hydrocarbon solvents. In accordance with this improvement finely divided alkali metal is suspended in a hydrocarbon and the ester to be reduced, together with the hydrolytic alcohol, are added to the alkali metal suspension. In order to insure complete reduction of the ester an excess of both the alcohol and the alkali metal is used. While this improvement has resulted in an increase in yield and some increase in reduction efiiciency, nevertheless it still permits considerable amounts of gaseous hydrogen to be evolved, which constitutes a waste of alkali metal. To decrease the amount of alkali metal lost by hydrogen evolution it has been proposed to operate the reaction under hydrogen pressure. This method, however. has not resulted in high reduction eniciencies on a commercial scale.

An object of this invention is to provide an improved method for reducing esters to produce high molecular weight alcohols by reaction with alkali metal and aliphatic alcohol which will result in high sodium reduction efficiencies and high yields of the product. A further object is to provide an improved method for reducing esters of resin acids to produce the corresponding alcohol, e. g., abietyl alcohol. Other objects will be apparent from the following description of our invention.

We have discoveerd that the reaction of alkali metal and hydrolytic alcohol on high molecular weight esters may be carried out with substantially no side reaction between the hydrolytic alcohol and sodium to evolve gaseous hydrogen if the ratio between the alcohol and the ester added to the reaction mixture is at all times equal to not more than two moles of hydrolytic alcohol for each mole of ester group to be reduced. Our improved process is distinguished from the prior methods in one respect by the fact that whereas prior methods used an excess of alcohol so that the alcohol functioned both I as reactant and as solvent, in our process the alcohol functions only as reactant and does not exist in excess. In fact in our process, there is at all times substantially no free hydrolytic alcohol in the reaction mixture, since the alcohol reacts substantially as fast as it is added to the reaction mixture to form alkali metal alcoholate.

We have further discovered that improved results may be obtained by using secondary or tertiary alcohols as hydrolytic alcohols in the herein described reduction process. The use of these alcohols results in better yields of pro not and more satisfactory operation, as more iully explained hereinafter.

In practicing our invention it is important that the hydrolytic alcohol and the esters to be reduced be added substantially simultaneously to the alkali metal and that there be no large excess of either alcohol or ester during the opera tion. If some of the alcohol should be added before adding the ester, or if the alcohol is added in excess of that required to reduce the ester present, the excess alcohol will react with the alkali metal to evolve hydrogen, thus resulting in a waste of the alkali metal. On the other hand, we have found that if the ester-is added to the sodium in the absence of the hydrolytic alcohol, the ester reacts with the alkali metal to form certain polymeric compounds (acyloins) which will not thereafter take part in the desired reaction.

In practicing our invention we prefer to use close to the theoretical amounts of alkali metal (that is, 4 gram atoms per mole of ester group to be reduced), or at most only a slight excess, e. g. 1% excess to take care of traces of water or other reactive impurities which may be present. As mentioned above, a substantial excess of alkali metal may be used if desired without deleteriously affecting the reaction. If an excess of sodium over that required for reduction of the ester is used, then hydrolytic alcohol equivalent to the excess sodium may be employed without deleterious effect. In this case there will be an equivalent wastage of hydrogen. However the use of excess alkali metal ordinarily is of no advantage in practicing our invention and generally results in a loss of metal because of the difficulty of recovering unreacted metal after the reaction has been completed.

It will be apparent that various methods may be used to bring the ester, hydrolytic alcohol and alkali metal into reaction in accordance with our invention. We prefer first to form a suspension of finely divided alkali metal in a hydrocarbon solvent such as xylene and to add to this suspension with eflicient agitation a hydrocarbon solvent solution of the ester to be reduced together with the hydrolytic alcohol in the ratio of 1 ester equivalent to 2 moles of the hydrolytic alcohol. The alcohol-ester solution is added slowly with rapid agitation, while the reaction mixture is heated or cooled as required to maintain the desired reaction temperature.

The temperature of the reaction mixture may vary between wide limits, for example from ordinary room temperatures ofaround 20-30 up to the boiling point of the solvent. cases we have found that the best yields are obtained by using a reaction temperature above the melting point of the alkali metal, e. g. above about C. when using sodium as the alkali metal. In the reduction of esters of resin acids by our invention, we prefer to use a higher reaction temperature than that preferably used for the reduction of fatty acid esters as described in our copending application Serial No. 729,900. For example, in the reduction of rosin esters such as methyl abietate or ester gum (glyceride of rosin), we prefer to maintain the reaction temperature in the neighborhood of to C.

After the reaction is complete, a small amount of a lower aliphatic'alcohol, e. g. methanol, is added to decompose any traces of unreacted sodium whichsmay be present. Water or acid, e. g. dilute sulfuric acid, then is added to decompose the alcoholates present. The acid solution should be added cautiously with rapid agitation and cooling as necessary. The reaction mixture then is washed with water to remove sulfates and distilled to separate the reaction product from the solvent. We prefer to distill oil. the hydrocarbon solvent at atmospheric pressure and In most then to distill off the product in a pure form by vacuum distillation.

We have found that the herein described method is especially well adapted for the preparation of higher alcohols by the reduction of esters of resin acids, for example esters of abietic acid. Various high molecular weight alcoholic bodies may be thus prepared by the reduction of esters obtained by the esteriflcation of various resinous products derived from wood and other natural sources, for example rosin and pine oil distillates. Likewise, esters of purified resin acids, e. g., abietic acid, pimaric acid and organic acids of like nature may be advantageously reduced to the corresponding alcohols by the herein described process.

The following examples illustrate specific methods of practicing our invention:

Example 1 Methyl abietate, 500 grams, was dissolved, together with 252 grams of secondary butyl alcohol. in 750 cc. of dry xylene. This solution was slowly added to a suspension of 152 grams of sodium in 750 cc. of hot xylene, with constant stirring, while the reaction mixture was maintained at a temperature of 128 to 130 C. After the reaction was complete, water was added to hydrolyze the alcoholates and the xylene layer was separated from the aqueous part. Abietyl alcohol was separated from the xylene solution by distillation. The yield of alcohol, was 357 grams, corresponding to 78.2% of the theoretical yield.

Example 2 The procedure of Example 1 was repeated, except that 241 grams of tertiary butyl alcohol was used as hydrolytic alcohol. The yield of abietyl alcohol was 83% of the theoretical.

Example 3 Grams Ester gum 500 Sodi Sec. butyl alc 226 The yield of crude abietyl alcohol was 303 grams or 66.3% of the theoretical yield.

Example 4 A mixture of esters was prepared by reacting methanol with Indusoil, a liquid product made and sold by the West Virginia Pulp and Paper Co. of Covington, West Virginia, under ester-H ing conditions. IndusoiP' apparently is a liquid mixture derived from wood, and contains fatty acids and acids of wood origin similar to abietic acid.

One ester equivalent (352 grams) of the ester!- fied Indusoir, together with two moles (176 grams) of tertiary amyl alcohol were dissolved in 500 cc. of xylene. This mixture was then slowly run into a boiling, constantly stirred, suspension of 115 grams of sodium in 1000 cc. of xylene. Thirty minutes were required for this addition and the reaction mixture then was stirred for an additional thirty minutes. The lmreacted sodium was decomposed with a slight excess of methanol and then water was cautiously added to take the alkali into an aqueous phase. The resulting mixture of alcohols then was recovered by distillation. The yield was 86.1% of theory of a liquid, boiling mainly at 170-90 C. at 2 mm. pressure. Free acid, 3.9%; acetyl value, 163; and Wijs iodine number of the acetyl derivative, 128.

Example 5 Methyl hydro-abietate (iodine, number Hubl, 57.4) was prepared by catalytically hydrogenating rosin and esterifying the hydrogenated product. A portion (316 grams) of the ester was reduced as in Example 4, using 220 grams of tertiary amyl alcohol .and 104 grams of metallic sodium. The resulting yield of hydro-abietyl alcohol was 228 grams, or 79.3% of theory.

In practicing our invention it is important that sufficient of a hydrocarbon solvent or other suitable solvent, is used in proportion to the amount of ester to be reduced, in order to prevent the excessive increase in the viscosity of the reaction mixture. The increase in viscosity of the reaction mixture as the reaction proceeds appears to be due to the various alkali metal alcoholates which are formedby the reaction. As shown by the equation given above, three alkali metal alcoholates may be formed, namely (a) from the hydrolyticalcohol used (b) from the alcohol component of the ester and (c) the alcoholate of the higher molecular weight alcohol produced by reduction of the ester. We have found that alkali metal alcoholates are insolu ble or only slightly soluble in hydrocarbon solvents. In general, the alkali metal alcoholates of the lower alcohols, e. g. ethyl alcohol, are substantially insoluble in most hydrocarbon solvents, while those formed from higher alcohols and especially branched chain higher alcohols have a considerable degree of solubility which tends to increase in proportion to their molecular weights. In most cases it would be practically impossible to use suflicient hydrocarbon solvent to dissolve more than a small portion of the alcoholates formed by the reaction. If the alcoholate is formed by a reaction of alkali metal with the alcohol in the presence of the hydrocarbon solvent, an insoluble precipitate forms which is more or less gelatinous in nature and greatly increases the viscosity of the mixture. On the other hand, we have found that when the alcoholates are formed by reacting sodium with the alcohol and the ester in substantially the theoretical proportions, the alcoholates produced are formed chiefly in the form of colloidal suspensions, that is, in the form of sols rather than gels and hence increase the viscosity to only a relatively small extent. The amount of solvent required in the reduction of a given amount of ester depends therefore on the alcohol component of the ester and on the alcohol used as hydrolytic alcohol. For example, we have found that the formation of sodium methylate in the reaction mixture tends to increase the viscosity of the mixture to a greater extent than the alcoholates of higher alcohols; hence in general, smaller amounts of solvent are required in the reduction of the glycerides than in the reduction of methyl esters of the high molecular weight acids. As regards the hydrolytic alcohols to be used, as stated above, those of higher molecular weight form alkali metal alcoholates which are somewhat more soluble in hydrocarbon solvents than those formed from a lower molecular weight alcohol. The alkali metal compounds of methanol, for example, are highly insoluble in hydrocarbon solvents and for this reason methanol is not recommended as hydrolytic alcohol. Other alcohols such as ethanol and normal butanol may be used with good. results, however, providing that the concentration of the ester to be reduced is kept 'sufliciently low and an excess of hydrolytic alcohol is avoided.

We have discovered that the use of alkali metal alcoholates of secondary and tertiary alcohols, i. e. alcohols having two or more carbon atoms attached to the carbon atom to which the hydroxyl group is attached, permits a much greater amount of a given ester to be reduced in a given amount of a hydrocarbon solvent than the alcoholates of normal alcohols of the same molecular weights. For example, when using either tertiary or secondary butyl alcohol as the hydrolytic alcohol in the reduction of the higher fatty acid esters in accordance with our invention and using xylene asa solvent, good results may be obtained with a concentration of 38 grams of a glyceride per cc. of solvent. On the other hand, if ethanol or normal butyl alcohol is used as the hydrolytic alcohol, the

concentration of glyceride cannot be more than 10 to 15 grams per 100 cc. of solvent; if the concentration is higher than this, the reaction mixture becomes too viscous to permit eflicient stirring before the reaction is completed.

The employment of the aforementioned secondary and tertiary alcohols in accordance with our invention is not restricted to the alkali metal reduction processes where the ratio of hydrolytic alcohol to ester is limited as described above. The above enumerated advantages accruing from the use of the secondary or tertiary alcohols may be obtained over a wide range of ratio of hydrolytic alcohol to ester. Furthermore, the addition of secondary or tertiary alcohol to a reaction mixture employing a primary alcohol will give improved results the degree of improvement depending chiefly upon the proportion of secondary or tertiary alcohol present.

Various organic liquids, inert to alkali metals and having boiling points sufficiently high to allow of their use at the desired reaction temperatures, may be used as solvents in accordance with our invention. Examples of suitable solvents are aromatic hydrocarbons such as xylene or toluene and aliphatic hydrocarbons, e. g. petroleum fractions, aliphatic ethers, e. g. dibutyl ether, tertiary amines, etc. If the-solvent selected contains substances reactive with alkali metal, an excess of the metal should be used to allow for the consequent side-reactions, or, preferably, the solvent should be purified before use, e. g. by treatment with sodium to remove the reactive constituents.

An important advantage of our novel method resides in the discovery that it permits reduction of unsaturated esters with little or no reduction of the ethylenic linkages, thereby resulting in the production of unsaturated higher alcohols, which have useful properties. Heretofore it has not been possible to reduce the unsaturated esters with alcohol and alkali metal without materially reducing the double bonds. A further important advantage is that substantially no free hydrogen is evolved, waste of alkali metal and hydrolytic alcohol is avoided, the material cost is decreased and the process is consequently more eflicient than prior methods. A further advantage resides in the employment of secondary and tertiary alcohols, e. g. secondary or tertiary butyl alcohohas hydrolytic alcobe used in practicing our invention it desirable.

However, such additional measures ordinarily are of no advantage in our process.

We claim:

1. A process for the reduction of abietic acid comprising dissolving an ester of abietic acid and a butyl alcohol in the ratio of approximately two moles of the alcohol to one mole of the ester in xylene and reacting the solution with approximately four gram-atoms of sodium per 'grammole of said ester suspended ina liquid hydro carbon having a boiling point above 100 0., at

a temperature of about 120 to 135 C.

2. A process for the reduction of abietic acid comprising reacting an ester of said acid simultaneously with alkali metal and the approxh mately theoretical quantity of a hydrolytic alalkali metals at a temperature of 120 to 135 C.

NORMAN DI. sco'rr. VIRBIL L. HANSLEY.

- cohol in a solvent medium substantially inert to 10 

